1. Field of the Invention
This invention relates generally to tape recorders, and more particularly is directed to an improved apparatus for changing the operating modes of a tape recorder.
2. Description of the Prior Art
It is known, for example, as disclosed in U.S. Pat. No. 3,976,263, to employ the motor-driven capstan shaft of a tape recorder as the source of the driving force required for establishing a selected mode of operation. In that way, only a relatively small manually applied force need be exerted on a push-button for selecting a respective mode of operation, and the major force for displacement of various elements required in establishing the selected mode is obtained from the capstan shaft. Thus, for example, the motor-driven capstan shaft may be employed as the source of the driving force for moving the magnetic head mounting plate or carriage to its operative position when establishing the playback mode in which the magnetic head or heads engage the tape and the pinch roller is pressed against the rotated capstan with the tape therebetween. In order to obtain such driving force from the motor driven capstan, it has been proposed to rotatably couple a first gear with the motor-driven capstan for rotatably driving a second gear when in meshing engagement with the latter, with the second gear having a toothless portion to permit rotation of the first gear with the capstan independently of the second gear when the latter is disposed in a rest position with its toothless portion facing the first gear. An actuator assembly adapts the tape recorder for a respective function thereof, for example, moves the head mounting plate or carriage to its operative position for establishing the playback mode of the tape recorder, in response to turning of the second gear. A latching assembly normally holds the second gear in its rest position and is actuable, for example, in response to manipulation of a push-button for selecting the playback mode, to permit an angular displacement of the second gear from its rest position into meshing engagement with the first gear so as to be driven by the latter in a substantially complete revolution, whereupon the latching assembly again holds the second gear substantially in its rest position.
With the foregoing arrangement, it is, of course, intended that the second gear should be in its rest position, and thus disconnected from the first gear, at any time when the power supply is first turned on or connected to the capstan driving motor. If such is the case, then the described arrangement for moving the head mounting plate or carriage to its operative position will not impose an excessive load on the motor driving the capstan at the time when the power supply is initially connected to such motor. However, if the power supply is disconnected or turned off shortly after the second gear has been brought into meshing engagement with the first gear, that is, prior to the completion of the movement of the head mounting plate or carriage to its operative position in response to selection of the playback mode, the capstan driving motor may come to rest with the second gear still in meshing engagement with the first gear. In that event, there will be an undesirably high torque loading on the motor when the latter is again connected to the power supply, and such loading may stall the motor.
The foregoing problem can be avoided by continuing the rotation of the capstan and its driving motor for a period of time sufficient to complete substantially a full revolution of the second gear, and thereby return the latter to its rest position disengaged from the first gear, even when the power supply has been disconnected from the capstan drive motor shortly after the second gear has been initially engaged with the first gear. In order to provide for such continued rotation of the capstan drive motor after the power supply has been discontinued therefrom, it has been proposed to increase the inertia of the motor either by increasing the diameter of a flywheel connected therewith or by increasing the rotational speed of the motor. Alternatively, it has been proposed to provide a capacitor in the circuit by which the power supply is connected with the capstan drive motor so that a charge accumulated on the capacitor during operation of the motor will continue to drive the motor for a suitable period of time after the power supply has been disconnected therefrom. However, increasing the size of the flywheel is undesirable in that it increases the cost of the tape recorder and also its size and weight. Providing a capacitor, as aforesaid, is also relatively expensive and space-consuming in that a large capacitance, for example, as large as 10,000 .mu.F, is required. The proposal to increase the speed of rotation of the capstan drive motor is also undesirable in that it requires reduction of the diameter of the capstan to maintain the standard tape speed or recording and reproducing. The capstan of reduced diameter may not have the requisite strength for reliable operation, particularly when subjected to the continuous pressure of the pinch roller.